More tests for the relationship
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
Fixed relationships and improved the tests.
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
TA484: made links in the view for going back and forth between book and authors.
Improved the model with functions
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL
Fixed a small bug in the 'has_book?' method.
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/ADL